The susceptibility of several malignant, spontaneously transformed, virus-transformed, and normal cell lines from different animal origins to cytotoxic induction by reoviruses was examined. The malignant and the majority of transformed cell lines were found to be susceptible to CT-induction. While virus adsorption is necessary, it does not play a major role in the phenomenon. In contrast, CT-induction could be related to agglutinability with concanavalin A. Experimental data suggest that the cell membrane appears to play a vital role in the CT phenomenon.